Ultrasonic dishwasher

ABSTRACT

Apparatus for supplying ultrasonic energy to a dishwasher consisting of a piezoelectric transducer arrangement associated with the washer chamber and a saturable core transformer, inverter-type circuit for energizing the transducers at high frequencies. Line voltage is utilized as the power source and &#39;&#39;&#39;&#39;ripple voltage&#39;&#39;&#39;&#39; provides variation in the inverter output frequency to prevent standing waves of ultrasonic energy in the washer chamber.

United States Patent 3,500,089 3/1970 Brech etal Robert D. BrubakerSeven Hills, Ohio 730,398

May 20, 1968 June 1, l 97 1 The Tappan Company Manslleld, Ohio inventorA ppl. No. Filed Patented Assignee ULTRASONIC DISHWASHER 4 Claims, 4Drawing Figs.

310/8.1,321/4S,259/1 int. Cl. "01v 7/00 Field 01 Search References CitedUNlTED STATES PATENTS 3,177,416 4/1965 Pijls et a1. 318/118 3,223,90712/1965 Blok et a1 318/118 3,296,511 1/1967 Van der Burgt et a1 318/1163,318,578 5/1967 Branson 259/1 3,360,710 12/1967 Barthoid.... 32l/4UX3,371,233 2/1968 Cook 310/8.1

3,448,370 6/1969 Harrigan 321/45 3,460,025 8/1969 De Prisco 321/45XPrimary Ekaminer-D. F. Duggan Attorney-Oberlin, Maky, Connelly andRenner ABSTRACT: Apparatus for supplying ultrasonic energy to adishwasher consisting of a piezoelectric transducer arrangementassociated with the washer chamber and a saturable core transformer,inverter-type circuit for energizing the transducars at highfrequencies. Line voltage is utilized as the power source and ripplevoltage" provides variation in the inverter output frequency to preventstanding waves of ultrasonic energy in the washer chamber.

PATENTED JUN 1 19?:

sum 1 or 2 \LL\Y\\\\\\\ AHHHHHI I I INVENTOR ROBERT D. BRUBA/(ERATTORNEYS BY W PATENTEDJUN nan 35821733 sum 2 BF 2 n m I l 4 DCVOLTS-INCREASE NOLLVUBdO 5O AQNHHOBHJ INVENT( )R ROBERT D. BIN/BAKER o(D (O ATTORNEYS ULTRASONIC DISHWASHER DISCLOSURE This invention relatesto ultrasonic dishwashers and more particularly to electronic circuitsfor energizing ultrasonic transducers in a varying frequency mode ofoperation.

The art of ultrasonic cleaning has received much considera tion in thepast and has become of importance in the domestic dishwasher field ofinterest. One of the significant considerations in this type ofcommercial embodiment is the attention which must be directed to aneconomical and simplified arrangement for producing the desired resultscommensurate with effectiveness of cleaning.

It is well known that ultrasonic cleaning operates on the principle ofcreating cavitation and vibration in a cleaning medium to effecta-separation of soil particles from dishware and the like and to providea measure of emulsification of oils and fats. The cavitation effectrelates specifically to the action which occurs at the interface betweenthe soil and the item of dishware and its effect is directlyproportional to the impedance difference occurring thereat. Vibrationeffects set up by the cleaning medium occur as energy waves which travelthrough the soil particles primarily normal to a particular interface.Both of these effects are further aided by the emulsification of fattymaterials which aids the separation of the soil particles and effects adispersion of same throughout the cleaning medium.

It is also known that the efficiency of the cleaning operation isdependent upon the manner of application of such ultrasonic energy.

Thus, in cavities such as a dishwasher enclosure, a specificdistribution of the energy will occur, dependent upon the frequency ofoperation and the physical characteristics of the cavity, such thatnodes of energy or the appearance of standing waves will occur. Suchcondition will cause localized cleaning effects and the avoidance ofsuch condition has received much attention in the prior art. For such afrequency dependent system, it would be desirable to modulate thefrequency of energization of the transducers to, in effect, sweep theapplied frequency about an optimum level of opera tion. Such approachwill cause a condition of continuously changing wave patterns related tothe sweep frequency of the system and if sufficient variance isprovided, an effective cleaning operation can be obtained.

The prior art indicates that this effect has been accomplished, forexample, by the utilization of two or more signal generating systemswherein generator outputs are combined to achieve some form ofmodulation or sequential switching of the generators may be performed toprovide a variable frequency condition. Further, substantial effortshave been directed toward combining an electrical frequency generatorfor energizing an ultrasonic transducer with mechanical means fordisturbing the system to provide a random and constantly varyingdistribution of the energy within the cavity. Most of these systemsrequire a substantial amount of apparatus and are unduly expensive andcomplicated and it is a primary object of this invention to provide animproved ultrasonic frequency generator which has a sweep provisioninherent therein and which is more economical and dependable than priorart systems.

It is another object of this invention to provide an improved ultrasonicfrequency generator which utilizes semiconductor and passive componentsentirely within the circuit and which receives its source of supply fromthe readily available household power lines. It is a further object ofthis invention to provide an improved ultrasonic frequency generatorwhich is more efficient and reliable than previous known devices andwhich may be readily incorporated in a commercial appliance.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principle of the invention may beemployed.

In said annexed drawings:

FlG. l is a cross-sectional side view of a dishwasher enclosure showingthe relationship of the ultrasonic transducers to the cleaning cavity;

FIG. 2 is a cross-sectional front view of the dishwasher of FIG. 1;

FIG. 3 is an electrical circuit diagram of the preferred embodiment ofthis invention shown in relation to a typical load arrangementcomprising six ultrasonic transducer crystals;

FIG. 4 is a graph showing the output frequency of the electrical circuitas related to impressed DC volts.

Referring now to FIGS. 1 and 2, there is shown a dishwasher 10 which isa typical application for the teachings of this invention. lt should beunderstood, however, that this invention may be applicable as well toother types of cleaning devices or forms of apparatus which rely on theapplication of ultrasonic energy to perform some useful function. Thedish washer 10 is shown mounted in an opening 12 within cabinet 13 andcomprises a water tight sheet metal enclosure 14 having essentiallyvertical front and rear walls l5, 16 respectively, a cylindrical bottom17 joined directly to the rear wall 16, and to the front wall 15 by ashort sloping section 18, and side panels 19, 20 of matchingconfiguration. The enclosure 14 forms the dishwasher cavity 22 forreceipt of the dishware to be cleansed. A control knob 24 is located onthe front panel 25 of the cabinet 13 and although not shown in thedrawings it will be understood that the electrical and electroniccontrol apparatus as well as a motor, pump and the like may beconveniently located in the cabinet 13 beneath the dishwasher enclosure14 or in any other nearby location. For purposes of illustration, thedishwasher 10 is shown with a wash load including a plurality of plates26 supported in position by a rack 27 in the lower portion of the cavity22, a plurality of cups 28 positioned at the upper portion thereof, anda silverware basket 29 disposed near the front wall 15 of the dishwashercavity 22. A fluid connector 31 is mounted in a depressed portion 32 ofthe bottom 17 of the enclosure 14 and such connector 31 may form thedrain outlet and the water inlet for the transferral of the cleaningmedium into and out of the dishwasher cavity 22.

A plurality of transducers 35 is mounted to lower exterior portions ofthe dishwasher enclosure 14 and in the description of the electricalportion of this invention, reference will be made to the utilization ofsix transducers. It will be appreciated that a greater or lesser numbermay be employed depending upon the relative efficiency required in thesystem, the power levels of operation and the like. Each transducer 35is of the electrostrictive piezoelectric type consisting of a bariumtitanate crystal and mounting arrangement and it will be understood thatother types of transducers may be employed as well under the teachingsof this invention.

A cover 37 for the dishwasher cavity 22 is shown in the closed positionbeing pivotally mounted to the top of the cabinet 13, as generallyindicated at 38, and the cover 37 may be swung to the open position foraccess to the dishwasher cavity 22. In normal operation, the cavity 22is filled with water as the cleaning medium to a level indicated by thedashed line 39 so as to completely submerge all of the items to becleansed. While the particular cleaning medium and the use of detergentsand the like are not of any great significance it should be understoodthat various loading arrangements of the dishwasher cavity 22 may havesome effect upon the electronic system in requiring greater or lesseramounts of power and in varying the frequency of operation. Such loadingeffect, however, is believed not a contributing factor to the properoperation of this system and is readily accommodated, the onlysignificance being the above-mentioned reflected condition imposed uponthe power supply which will be described in greater detail hereinafter.While the cleaning medium is retained within the cavity 22 duringultrasonic cleaning, it will be understood that various additionalcycles of rinsing and the like may be employed throughout the completecleaning operation.

In FIG. 3, there is shown a circuit schematic of this invention whereina source of power 40 which may be the typical 120 volt, AC 60 Hz.household power is connected through a fuse 41 to the input terminals42, 43 of a bridge rectifier 45. The output of the rectifier appears atterminals 47, 48 and connected thereacross are capacitors 49, I whichprovide a measure of filtering and high frequency bypass, respectively,so that essentially a DC voltage is realized for energizing the circuit.As will be pointed out in greater detail hereinafter, the DC voltageappearing at terminals 47, 48 includes a rather large ripple voltage oftwice the frequency of the power source 40 and which is utilized incontrolling the output frequency of the circuit.

An output transformer 50 having primary windings 51a, 51b with a centertap 52 and a secondary winding 53 is provided for converting the voltageappearing within the circuit to an optimum output voltage at terminals54, 55 and for providing electrical isolation. A load 56, comprising sixtransducers 35 in parallel connection is connected across the secondarywinding 53 of the transformer 50, such connection being made by leadwires extending from the area beneath the dishwasher cavity 22 to thearray of transducers 35.

The electrical circuit is basically a typical inverter circuit whichutilizes semiconductor components for alternately switching currentthrough the primary windings 51a, 51b of the transformer 50 at anultrasonic frequency. Such switched current is coupled to the transducerload 56 by the secondary winding 53 of the transformer 50 at a reducedvoltage level. The primary windings 51a, 51b of the transformer areconnected to lines 58, 59 respectively, the positive output terminal 48of the bridge rectifier is connected to center tap 52 and the negativeoutput terminal 47 is connected to ground 60 which forms a referencepotential for the circuit. The switching of current through the primarywindings 51a, 51b of the transformer 50 is achieved by theinterconnected switching action of a pair of NPN transistors 62, 63having respectivc collectors 62c, 630 connected to lines 58, S9 andemitters 62a, 63a connected through resistors 65, 66 to ground 60.

A saturable core transformer 68 is provided for achieving oscillationwithin the circuit and serves to couple the outputs of the transistors62,63 with the input circuit in a relationship suitable to achievingoscillation. The primary winding 68a of the transformer 68 is connectedat each end through resistors 69, 70 of approximately 800 ohms to thecollectors 62c, 630 of the transistors 62, 63, and thus, to each side ofthe primary windings 51a, 51b of the output transformer 50. Thesecondary windings 68b, 68c of the saturable core transformer include acenter tap connection 72 and are wound to have the phase relationshipindicated by the dots in FIG. 3. The ends of the secondary windings 68b,68c are connected to the base electrodes 62b, 63b, of the respectivetransistors 62, 63, through resistors 74, 75 of approximately ohmsresistance. Semiconductor diodes 76, 77 are connected from the baseelectrodes 62b, 63b of the transistors to ground potential 60 and arepoled in a direction to prevent a negative voltage from occurring at thebase electrodes.

A voltage divider consisting of series resistors 78, 79 having commonjunction 80 and including capacitor 82, bypass capacitor I01, and diode83 connected in parallel with resistor 79 is connected between groundpotential 60 and the positive output terminal 48 of the bridge rectifier45. The junction 80 of the voltage divider is connected directly to thecenter tap 72 of the secondary windings of the saturable coretransformer 68 and in normal operation provides a relatively low voltagewhich is on the order of approximately one volt to aid in the start upof the circuit and to avoid distortion of the output waveform at thetime of switching of the transistors 62, 63.

The circuit shown in FIG. 3 utilizes a parallel switching action toaccommodate relatively high power levels which are on the order ofapproximately 750 watts of input power. The parallel circuit consists oftransistors 85, 86 which are connected with identical circuitry inparallel with transistors 62, 63 respectively and which receive theswitching signals from the secondary windings 68b, 68c of thetransformer 68 by way of lines 87, 88. The circuit also includes athyrector 90 which is a back to back diode element, connected across theprimary windings 51a, 51b of the output transformer 50 to preventdestructive voltage transients from affecting the components of thecircuit, similar action being performed by the base to ground diodes 76,77 previously mentioned as well as diodes 91,92.

Thus, the operation of the inverter circuit of FIG. 3 occurs as follows.Upon switching on power a slight positive potential will appear at thejunction of the voltage divider and will cause either transistors 62, ortransistors 63, 86 to conduct due to inherent variances within thecircuit. It will be assumed that the potential at the base 62b oftransistor 62 will be increasing in a positive direction to causegreater conduction of transistor 62 and similarly, of transistor 85.Current will flow in the conventional sense from the positive terminal48 of the bridge rectifier 45 to the center tap connection 52 of thetransformer 50, through primary winding 51a, the collector to emitterpaths of transistors 62, 85, and the emitter resistors 65, 94 to groundpotential 60. Current flow will also occur through the primary winding68a of transformer 68 and due to the polarity of connection of thesecondary windings 68b, 68will serve to further increase the positivepotential at the base electrodes of transistors 62, 85 until saturationoccurs. In the opposite portion of the circuit, an inverse action willoccur such that the bases of transistors 63, 86 will be driven in anegative sense to completely out off collector to emitter con ductionand thus the flow of current through primary winding 51b. Whensaturation of transformer 68 occurs and no further current change takesplace, the voltage polarities at the secondary windings 68b, 68c of thetransformer will reverse and all transistors will be driven in theopposite sense such that transistors 63, 86 will be driven towardsaturation while transistors 62,85 are cut off to complete the cycle.

Thus, it may be seen that the primary windings 51a, 51b of the outputtransformer 50 will realize current flow from the center tap 52 toeither side alternately and this action will occur at a frequencydependent upon the voltage output of the bridge rectifier 45 and thesaturation characteristics of the saturable core transformer 68. If theDC voltage output of the bridge rectifier 45 and filter capacitor 49arrangement were a constant DC level, the inverter circuit would attaina nominal frequency of operation and only vary slightly from this leveldue to temperature effects and the like of the components within thecircuit. This condition also assumes that a fixed transducer load 56 isconnected across the secondary winding 53 of the output transformer 50such that the circuit characteristic impedance will be reflected back tothe transistor switching portion of the circuitry. [f the load 56 werevaried to some extent as by the connection of either a greater or lessernumber of transducers 35 or by the variation in loading of thedishwasher cavity 22 by means of, for example, a different water levelor different amounts or types of dishware therein, a correspondingslightly different frequency of operation would be expected and doesoccur.

Assuming, however, that all of these variables remain relativelyconstant, a substantially constant frequency of output voltage from theinverter circuit will be realized. As pointed out previously, when thetransducer 35 are energized in such a manner ultrasonic oscillations areset up within the dishwasher cavity 22 and a static condition ofdistribution of energy within the cavity will prevail. Localizedcleaning therefore, will occur and it will be clear that some locationswithin the cavity will achieve no cleaning effect due to theinterference of the standing waves where nodal effects occur. It is aprime object of this invention to avoid such static wave conditionswithin the dishwasher cavity to effect a more efficient cleaningoperation.

It has been determined that if the input voltage to the in vertercircuit at terminals 47, 48 is caused to vary about a nominal DC level,then a corresponding variation in the output frequency at terminals54,55 can be achieved.

Referring now to FIG. 4, it is shown that such a frequency variationoccurs in the output of the circuit, even though the reasons for thecircuit performance are not well understood at this time. FIG. 4 is agraph of the output frequency of the inverter circuit at the secondarywinding 53 of the output transformer 50, for a typical load 56configuration as that previ ously described, as the DC volts applied atterminals 47, 48 of the circuit are varied. A dashed line 95 is depictedon the graph and is indicative of the transducer-load resonant frequencywhich in this example will be assumed to be at a frequency of 25 kHz. Asthe DC level of voltage at terminals 47, 48 is increased in a positivesense, the frequency of operation of the circuit will increase also inan approximately linear manner as shown generally at 96. This would beexpected output variation from typical inverter circuit theory.

As the output frequency reaches a level of approximately 20 kHz., a snapshift in frequency occurs as indicated at 98, such that the frequency ofoperation suddenly shifts toward the load resonant level 95 without anyfurther increase in the input DC voltage. This snap shift 98 infrequency might also be expected in a circuit configuration of this typewherein a particular load arrangement has a relatively defined naturalfrequency of resonance. When the load 56 and circuit frequencies becomerelatively close, it would be expected that one would lock" onto theother or that a new frequency of resonance for the combination might beexpected. Along this line of reasoning, it should be assumed thatfurther variations in the DC input voltage would cause relatively littlefrequency deviation in the output voltage since the combination wouldtend to maintain the resonant frequency of operation.

However, it has been determined that input voltage variations willcreate a corresponding output frequency variation as indicated by line99 showing both an increase and decrease of output frequency as the DCvolts are varied about the snap shift level. This deviation from anominal level is a desirable attribute of this circuit in altering theultrasonic frequency realized from the transducers 56 and thus varyingthe standing wave pattern within the cleaning cavity to effect athorough cleaning operation.

Such input DC voltage variation is readily achieved in this particularcircuit since an alternating current power source 40 is utilized. It iswell known that the output of the bridge rectifier 45, withoutfiltering, is a full wave DC voltage varying in amplitude as the voltageof the AC source varies. In typical power supply circuits, it is usualto provide a filter to smooth this voltage completely to avoid ripplewhich is normally not desirable. Here, however, the ripple voltageprovides a voltage variation at terminals 47, 48 to alter the outputfrequency applied to the transducers and this is readily provided by aminimal filter arrangement consisting, in this embodiment, of a 200 mfd.condenser for capacitor 49, bypass capacitor 100 being on the order of0.1 mfd. This circuit is designed so that the ripple voltage present atthe output of the bridge rectifier 45 is about percent of the value ofthe voltage level that results in operation at transducer resonance. A 5percent frequency shift is achieved for such a 10 percent voltagechange.

Although AC voltage as the power source 40 provides a convenient signalfor varying the DC voltage at terminals 47, 48, it will be appreciatedthat such variations could be effected differently as by modulating thevoltage by a locally generated signal. Similarly, differenttransducer-load configurations and modifications of the circuitry arepossible while still realizing the sweep" frequency output feature ofthe described arrangement. Further, component values, frequency andpower levels specified herein relate to the preferred embodiment and maybe varied for different applications.

Other modes of applying the principles of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I, therefore, particularly point out and distinctly claim as myinvention:

1. In combination with a load device, apparatus for producing ultrasonicvibrations in said load device at continuously varying frequencies,comprising a plurality of transducers coupled to said load device, saidtransducers being in parallel electrical connection and operative toconvert electrical energy to mechanical vibrations, an outputtransformer having a secondary winding connected to said transducers anda primary winding adapted for energization, a first pair of switchingelements connected to said primary winding for controlling current flowtherein, a second pair of switching elements operatively connected inparallel with said first pair of switching elements, a saturable coretransformer operatively connected with said switching elements foralternate energization thereof, the primary winding of said saturablecore transformer being operatively connected with the primary winding ofsaid output transformer, the frequency of alternation being dependentupon the magnitude of voltage applied to said switching elements, meansfor supplying DC voltage to said switching elements for energizing sameat a nominal frequency of alternation, and means for effecting cyclicalvariations in the DC voltage to cause variations in the frequency ofalternations.

2. The combination set forth in claim 1 wherein said switching elementscomprise transistors having collector electrodes connected to theprimary winding of said transformer and adapted for energization fromsaid saturable core transformer.

3. An ultrasonic dishwasher, comprising a housing forming an enclosurefor receipt of dishware and the like and a fluid medium, a plurality ofpiezoelectric transducers mounted on the exterior of said housing forgenerating ultrasonic vibrations in the fluid medium contained therein,an inverter circuit for energizing said transducers, said circuit havinga nominal frequency of operation in the ultrasonic frequency range andcomprising an output transformer having a secondary winding connected tosaid transducers, a first pair of transistors having collectorelectrodes connected to the primary winding of said transformer, asecond pair of transistors operatively connected in parallel with saidfirst pair of transistors for energizing the primary winding of saidtransformer, and a saturable core transformer having a primary windingoperatively con nected to said collector electrodes and a secondarywinding operatively connected in the base-emitter paths of saidtransistors, and means for energizing said inverter circuit with a DCvoltage having a high ripple voltage, comprising an AC power source, arectifier, and filter capacitor combination, said filter capacitorhaving a capacitance value to provide approximately 10 percent ripplevoltage, whereby said transducers will provide ultrasonic vibrations inthe fluid medium at frequencies continually varying about such nominalfrequency.

4. A dishwasher as set forth in claim 3 wherein said rectifier is abridge rectifier, said power source is 60 cycle alternating current andthe frequency of the ripple voltage is cycles per second.

1. In combination with a load device, apparatus for producing ultrasonicvibrations in said load device at continuously varying frequencies,comprising a plurality of transducers coupled to said load device, saidtransducers being in parallel electrical connection and operative toconvert electrical energy to mechanical vibrations, an outputtransformer having a secondary winding connected to said transducers anda primary winding adapted for energization, a first pair of switchingelements connected to said primary winding for controlling current flowtherein, a second pair of switching elements operatively connected inparallel with said first pair of switching elements, a saturable coretransformer operatively connected with said switching elements foralternate energization thereof, the primary winding of said saturablecore transformer being operatively connected with the primary winding ofsaid output transformer, the frequency of alternation being dependentupon the magnitude of voltage applied to said switching elements, meansfor supplying DC voltage to said switching elements for energizing sameat a nominal frequency of alternation, and means for effecting cyclicalvariations in the DC voltage to cause variations in the frequency ofalternations.
 2. The combination set forth in claim 1 wherein saidswitching elements comprise transistors having collector electrodesconnected to the primary winding of said transformer and adapted forenergization from said saturable core transformer.
 3. An ultrasonicdishwasher, comprising a housing forming an enclosure for receipt ofdishware and the like and a fluid medium, a plurality of piezoelectrictransducers mounted on the exterior of said housing for generatingultrasonic vibrations in the fluid medium contained therein, an invertercircuit for energizing said transducers, said circuit having a nominalfrequency of operation in the ultrasonic frequency range and comprisingan output transformer having a secondary winding connected to saidtransducers, a first pair of transistors having collector electrodesconnected to the primary winding of said transformer, a second pair oftransistors operatively connected in parallel with said first pair oftransistors for energizing the primary winding of said transformer, anda saturable core transformer having a primary winding operativelyconnected to said collector electrodes and a secondary windingoperatively connected in the base-emitter paths of said transistors, andmeans for energizing said inverter circuit with a DC voltage having ahigh ripple voltage, comprising an AC power source, a rectifier, andfilter capacitor combination, said filter capacitor having a capacitancevalue to provide approximately 10 percent ripple voltage, whereby saidtransducers will provide ultrasonic vibrations in the fluid medium atfrequencies continually varying about such nominal frequency.
 4. Adishwasher as set forth in claim 3 wherein said rectifier is a bridgerectifier, said power source is 60 cycle alternating current and thefrequency of the ripple voltage is 120 cycles per second.